Tone combination detector and coincidence timer circuit
US4042789A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | May 17, 1976 |
| Grant date | Aug 16, 1977 |
| Priority date | — |
| Expiry date | May 17, 1996 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04Q1/457
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
A tone receiver for detecting a Dual Tone Multi-Frequency (DTMF) signal includes first and second digital tone detectors for the high and low bands, respectively. These detectors are of the type which employ the period detection technique. Each detector has a set of outputs corresponding to the valid tones in the respective band. A latching flip-flop is associated with each output of each detector. A coincidence timer is provided to insure that there are outputs from each of the detectors for a predetermined duration of time. The coincidence timer is reset by any change of any of the latching flip-flops from a state representing absence of the tone to a state representing presence of such tone. The latching intervals are determined by zero-crossings, which define the periods involved in the period detection operation.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.